A MEMS (Micro Electro Mechanical Systems) structure in which an excitation section including a piezoelectric thin film is formed on a Si semiconductor layer has been known. For example, Patent Document 1 cited below discloses a vibration device in which each one end of a plurality of vibration arms is connected to a support member. In this vibration device, the vibration arms each include a Si semiconductor layer. A SiO2 film is provided on the Si semiconductor layer. On the SiO2 film, a first electrode, a piezoelectric thin film, and a second electrode are laminated in that order. In other words, an excitation section including the piezoelectric thin film is formed on the Si semiconductor layer.
The vibration device disclosed in Patent Document 1 is a vibration device making use of bulk waves. Further, the vibration device disclosed in Patent Document 1 includes a relatively thick SiO2 film of no less than 2 μm in order to improve temperature characteristics.
Meanwhile, Patent Document 2 cited below discloses a surface acoustic wave semiconductor device using an n-type Si substrate doped with phosphorus (hereinafter, referred to as “P”). It is described therein that using the n-type Si substrate doped with P makes it possible to change an elastic constant, a velocity of the surface acoustic wave, and the like, and improve temperature characteristics.
Patent Document 2: U.S. Pat. No. 8,098,002
Patent Document 3: Japanese Unexamined Patent Application Publication No. 57-162513